1. Field of the Invention
The present invention relates to a method of removing material from a surface in a vacuum chamber by using plasma-activated hydrogen.
When coating workpieces it is for instance often necessary to subject the support for the workpiece to a cleaning process prior to the coating in order to be in a position to precipitate thereafter the coating to be deposited with a high adherent strength Such a method is applied in all such cases where workpieces are to be coated by means of a vacuum process such as for a coating of semiconductor circuits or for instance tools. Further applications of the method encompass the removal of contaminations not only from the workpieces but also from the vacuum chamber itself. The field of such a cleaning procedure covers the removal of contaminations consisting of oxides, carbon and also carbon compositions whereby the chemical reactivity of the hydrogen is utilized.
2. Description of the Prior Art
Known cleaning methods for workpieces are for instance plasma etching processes and atomizing etching processes. When the above mentioned methods involve high etching rates, it is possible that temperatures of several 100.degree. Celsius are encountered at the workpiece. In many cases such high temperature values are not suitable for the workpiece. Additionally, relative high energy values of the particles by means of which the workpiece is treated in the range of several 100 electron volts are encountered. Apart from the high thermal loading such can lead to a change or to defects, in the surface structure of the workpiece. A further drawback of the known methods is that the etching process itself can cause a contamination of the workpiece by a recoating. By means of the known methods highest demands of purity can thus be achieved only within limits
In order to circumnavigate these drawbacks and to be in a position to use a more protective etching process it has been proposed to etch silicon dioxide by means of activated hydrogen such as disclosed in the publication of Arthur Sherman "In situ removal of native oxide from silicon wafers", technical journal J. Vac. Sci. Technol. B 8 (4), July/August 1990, page 656. According to this publication it is proposed to activate the hydrogen in a hollow cathode discharge at a discharge voltage of 600 Volts and a discharge current of 100 milli-amps. The there proposed arrangement does, however, not completely solve the above mentioned problems because the high electron energy of about 600 volts can lead to defects of the surface structure and to a re-coating by sputtering processes. A further technical publication of Y. Kunitsugun I. Suemune "Low temperature cleaning of Si and growth, of GaAs on Si by hydrogen plasma assisted metallorganic molecular beam epitaxy" of Journal of Crystal Growth 95 (1989) 91-95 North-Holland, Amsterdam discloses a further etching method for silicon and gallium arsenide surfaces, which operates with activated hydrogen, whereby here the activation of the hydrogen proceeds in a ECR-plasma. The generating of such ECR-plasma discharges with a microwave coupling is relatively costly and is difficult to realize specifically for large area applications. In case of high demands made at the homogenity of the distribution of the removal, this method is specifically intrinsic and the realization in case of very large dimensions, if possible at all, poses large problems.